Window Replacement Calculator

In 2026, uPVC casement windows typically cost £500-£700 each supply and install. Sash windows cost £800-£1,100 in uPVC or £1,400-£1,800 in timber. A full house replacement of 8-10 standard casement windows usually costs £4,500-£7,000 in uPVC or £8,000-£15,000 in timber.

Yes, replacement windows in England and Wales must comply with Part L thermal standards (U-value ≤1.4 W/m²K). Most installers are registered with FENSA or CERTASS, which provides self-certification. Otherwise you need a local authority building control application costing around £250.

uPVC windows typically last 20-25 years before the seals or mechanisms need attention. Timber windows can last 50+ years with regular maintenance (painting every 5-8 years). Aluminium windows last 30-40 years. Composite windows offer 30+ year lifespans with minimal maintenance.

The Energy Saving Trust publishes whole-home figures, not per-window ones. Replacing entirely single-glazed windows with A-rated double glazing saves roughly £140 a year for a typical semi-detached house (more for a detached home, less for a flat). Upgrading old double glazing to modern A-rated units saves much less — typically around £100 a year for the whole home — because the existing units already block most of the heat loss, so payback can run to several decades.

Most replacement windows fall under permitted development and do not need planning permission, provided they are similar in appearance to the originals. Listed buildings always require listed building consent. Conservation areas may require planning permission if the window appearance changes significantly.